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我正在使用带有休眠的弹簧数据。我有一个双向映射如下：

public class Student {
   ...
   @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true,    mappedBy="student")
   private List<StudentLog> logs = newArrayList();  
   ...
}

public class StudentLog {
   .....
    @ManyToOne(cascade = CascadeType.REFRESH, optional = false, fetch = FetchType.LAZY)
    @JoinColumn(name = "STUDENT_ID" , insertable = true, updatable = false, nullable =false)
    private Student student;
   .....
}

当我使用 JpaRepository 删除学生时： repo.delete(s.getId()); 我可以看到以下查询

Hibernate: select count(*) as col_0_0_ from STUDENTS student0_ where student0_.ID=? and 1=1
Hibernate: select student0_.ID as ID1_2_2_, student0_.FIRST_NAME as FIRST2_2_2_,  educationh1_.STUDENT_ID as STUDENT6_2_4_, educationh1_.ID as ID1_0_4_, educationh1_.ID as  ID1_0_0_, educationh1_.CLASS as CLASS2_0_0_, educationh1_.LEVEL as LEVEL3_0_0_, educationh1_.PREDICTED_END_DATE as PREDICTE4_0_0_, educationh1_.START_DATE as START5_0_0_, educationh1_.STUDENT_ID as STUDENT6_0_0_, educationh1_.TERM as TERM7_0_0_, logs2_.STUDENT_ID as STUDENT3_2_5_, logs2_.ID as ID1_3_5_, logs2_.ID as ID1_3_1_, logs2_.LOG as LOG2_3_1_, logs2_.STUDENT_ID as STUDENT3_3_1_ from STUDENTS student0_ left outer join EDUCATION_HISTORY educationh1_ on student0_.ID=educationh1_.STUDENT_ID left outer join STUDENT_LOG logs2_ on student0_.ID=logs2_.STUDENT_ID where student0_.ID=?
Hibernate: delete from STUDENT_LOG where ID=?
Hibernate: delete from STUDENTS where ID=?

知道为什么休眠会发出 2 个选择查询吗？没有选择就不能只发出删除查询吗？

谢谢

4

1 回答 1

1

JPA 仅公开了一个remove(…)方法，EntityManager该方法需要删除实体。因此，对于您使用 id 进行的调用，delete(…)我们首先检查具有 id 的实体是否真的存在（第一次查询）。然后我们具体化对象（第二个查询）以最终将其交给EntityManager.remove(…)（查询 3 和 4）。

实际上检查是多余的，因为我们可以在第二步exists(…)中简单地检查。null我已经创建并修复了 DATAJPA-363，因此您以后应该会少看到一个查询。

于 2013-06-27T21:05:01.693 回答